This invention relates (a) to the detection of sleep-disordered breathing, (b) to the differentiation of its various manifestations and to their timing and prevalence of occurrence, and (c) to associated cardiovascular impact. In this important health-assessment setting and field, the invention particularly features, for such detection and differentiation purposes, the novel use of an anatomy-attached, three-orthogonal-axis accelerometer as the principal agency for acquiring, in simultaneity, certain key, mechanical, multi-facet anatomical information, featuring highly-persuasive, three-dimensional, vector information, which is fundamentally relevant to finding and characterizing disordered breathing. The use of such an accelerometer has been discovered by us to yield data which, at least in part because of its three-dimensional vector nature, in relation to the best known prior art practices in this area, significantly improves the critical, detection and differentiation medical focus on, and understanding of, a multifaceted breathing condition which is serious, often elusive, and in some undetected and unmanaged circumstances, fatal.
Sleep disordered breathing is a condition characterized by repeated episodes of underbreathing (hypopnea) and not breathing (apnea). It is believed that a significant population of adults experience sleep-disordered breathing.
There are two main forms of sleep apnea—central and obstructive. Central sleep apnea is related to a dysfunction of the autonomous nervous system that reduces respiratory drive, and which can lead to long breathing pauses. Obstructed airway paths cause obstructive sleep apnea. The differential diagnosis of both forms of apnea is non-trivial, and multiple vital signs are needed to be recorded and analyzed, including the presence and frequency of snoring episodes as one of the helpful markers, in order to diagnose obstructive sleep apnea.
Both obstructive and central sleep apnea are associated with increased morbidity and mortality. Sleep-disordered breathing can cause temporary elevations in blood pressure in association with lowered blood oxygen levels, and may cause elevated blood pressure during the day, and eventually, sustained high blood pressure (hypertension). The medical complications of sleep apnea are associated with an increased prevalence of hypertension, heart failure, myocardial ischemia and infarction, arrhythmias and sudden death, often related to the lack of oxygen (hypoxia) and the abrupt increases in sympathetic tone associated with repeated apneic episodes. Also, previously unsuspected sleep apnea may contribute to the apparent refractoriness of cardiac disease and inability to adequately treat heart failure. Other symptoms include cerebrovascular accident and arrhythmias. In addition, the daytime sleepiness or somnolence associated with untreated sleep apnea constitutes a hazard to the public health because of its implications for driving and the operation of industrial machinery.
These considerations combined with the availability of effective therapeutic techniques like continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BIPAP) make it extremely important to detect sleep apnea and its complications accurately and confidently.
In the current state of the art, polysomnography is a well-established procedure to detect sleep apnea, but it is expensive and requires elaborate equipment and specially trained personnel. Therefore, it would be desirable to have a technique for detecting, differentiating and evaluating the cardiovascular effects of sleep apnea that is inexpensive, easy to use and that can be employed in a patient's home as well as in the hospital setting. The availability of such a convenient and cost-effective technique would make it possible to provide diagnostic evaluations for sleep apnea to many more patients than is currently feasible.
Furthermore, although traditional polysomnography provides detailed information about the various stages of sleep and wakefulness through brain activity (EEG) and eye movements (EOG), its ability to provide information about the cardiovascular complications of sleep apnea is extremely limited. This is especially important because of the inability of patients to report symptoms from events that occur during sleep. Therefore, furnishing objective evidence of previously unsuspected cardiovascular complications can alert physicians of the need to provide important treatment to patients who otherwise might not have received it.
The present invention is especially, though not exclusively, intended for both daytime and nocturnal monitoring applications. Preferably, it involves, combinationally, the cooperative, simultaneous “gathering”, in addition to a number, such as three, “leads” of ECG data, heart sounds and several other categories, or facets, of mechanical anatomical, three-dimensional, vector data derived from a single, suitably anatomy-attached, three-orthogonal-axis accelerometer. This combination of ECG, and three-axis-accelerometer heart sound and additional anatomical data, allows readily for the confident detection and differentiation of sleep-disordered breathing.
In connection with practice of the present invention, the fact that what is proposed involves a three-dimensional vector method utilizing a three-axis accelerometer, is important for various reasons, including the conditions that chest and abdominal movements don't simply have a normal component (z axis only) to the chest, and that gravity and body position each influence these movements. As well, in this setting, such vector information is important to supply accurate magnitude information for respiration evaluation. Three-dimensional spatial directionality of such vector information is important also in obtaining, for evaluation use, body posture information from a subject.
A key element in this vector practice of the present invention centers on the true, multi-faceted use of a three-orthogonal-axis accelerometer to gather, in simultaneity, a large family of mechanical information from a subject, from, and in relation to, which information it is possible to analyze, interpret and display, accurate, related heart sound, respiratory, posture and body-activity data facets in order thereby to provide clinical experts with powerful evaluation and assessment insights into a subject's cardio-pulmonary condition for both acute and chronic kinds of situations.
In the preferred and best mode implementation of the invention, an accelerometer, placed preferably at, or very closely adjacent, the well-recognized V4, precordial ECG chest site, performs all signal data gathering, except for the gathering of ECG electrical information which also plays a role in the practice of the invention. However, in some cases, it may be useful to employ an independent microphone for sound-collecting purposes. Such an independent microphone could be either a physically and spatially independent device, or it could be physically “package-integrated” with the employed accelerometer.
Given the state of the art today involving the making of extremely tiny mechanical and electromechanical structures, a three-orthogonal-axis accelerometer of the kind which is usable conveniently in the practice of the present invention, referred to also herein simply as a three-axis accelerometer, might typically have dimensions on the order of about 5×5×2-mms. Such a device might be “stand-alone” in nature, limited just to the basic acquisition of three-axis signal data, or it might be structured in combination (internally in an integrated package) with relevant, appropriate, algorithmically programmed, signal-data-processing and recording micro-circuitry, either “structural approach”, of course, coming with appropriate, readily externally accessible, signal-output connection structure(s).
In this connection, it will be immediately apparent to those skilled in the art that such an accelerometer, as well as all, appropriate signal-data-processing circuitry, including digital computer data-processing and recording circuitry, and algorithmic methodology (as such are described functionally and organizationally below both in high-level text and in block/schematic drawing form) needed to implement the data-handling processing and analyzing aspects of the invention, may be conventional in nature, and may take on a number of different, entirely adequate forms. The details of these matters do not form any part of the present invention, and they are, accordingly, not discussed or elaborated herein in great detail. Rather, they are mentioned in the practice of the invention, as just suggested, in appropriate, high-level disclosure terms.
Useful background information regarding such data-processing and algorithmic circuitry and methodology employing digital computer structure may be found in the following documents, the entire contents of which are hereby incorporated herein by reference: U.S. Pat. No. 7,096,060 to Arand et al., issued Aug. 22, 2006, for “Method and System for Detection of Heart Sounds”; U.S. Patent Application Publication No. 2007/0191725 of Nelson, published Aug. 16, 2007, for “Wavelet Transform and Pattern Recognition Method for Heart Sound Analysis”; and U.S. Patent Application Publication No. 2010/0094148 of Bauer et al., published Apr. 15, 2010, for “Differential Apneic Detection in Aid of Diagnosis and Treatment”. Signal-processing algorithmic methodology and other relevant matters described in these documents may be employed very satisfactorily in the signal-processing and data handling and analyzing environment associated with practice of the present invention.
Preferably, the main signal-gathering device, the three-axis accelerometer, will be located on the subject's chest in a position on the thorax, such as the one mentioned above, so it can easily pick up respiratory movement. Acquired data may be recorded onto associated digital media, such as onto an accelerometer-package-integrated SIM chip similar to those used in digital cameras, with such data being easily downloadable to an external computer.
According to a preferred and best-mode manner of describing the present invention, it proposes a method for monitoring sleep-disordered breathing including the steps of (a) collecting, simultaneously, multi-facet, three-axis data from a sleeping subject utilizing an anatomy-attached, three-orthogonal-axis accelerometer, and (b) following such collecting, processing and analyzing the collected data to detect associated, disordered breathing including assessing the presence of at least one of (a) sleep-disordered breathing generally, (b) sleep apnea specifically, (c) differentiation between central and obstructive sleep apnea, and (d) hypopnea.
The invention may also be expressed as a method for detecting sleep disordered breathing involving (a) using a three-orthogonal-axis accelerometer attached to a selected site on a subject's anatomy, collecting from that site, over a chosen, or selected, time interval, multi-facet, three-axis accelerometer signal data which may include, as collected components, two or more of activity, posture, heart sounds, snoring, and respiration, (b) independently facet-filtering this collected data through one or more independent, facet-specific filtering agencies which produce, respectively, filtered data reflecting, and specific to, one or more of the mentioned components, (c) selectively and combinationally processing and analyzing such filtered data, and (d) from the steps of processing and analyzing, producing output information associated with the selected anatomical site describing any detected sleep disordered breathing.
Added as steps to these representative, methodologic characterizations of the invention in a further embodiment are the additional steps of (a) simultaneously acquiring, during a chosen time interval such as the one mentioned above, ECG electrical data, and (b) including information contained in such acquired electrical data in the mentioned processing and analyzing steps.
Further included in the implementation of the present invention may be the practice, based upon the analyzing step, of producing, as output, at least presentable graphics information relating to at least one of (a) sleep-disordered breathing generally, (b) sleep apnea specifically, (c) differentiation between central and obstructive sleep apnea, and (d) hypopnea.
These and other important features and advantages of the invention will become more fully evident as its detailed description which follows shortly is read in conjunction with the accompanying drawings.
Timing information comes from the evident, simultaneously acquired, and thereafter conventionally marker-event processed, three-lead, ECG electrical data.
The report information presented in FIGS. 3-9, inclusive, and the various manners shown for presenting it, are basically conventional, and very familiar to those skilled in the relevant medical art, and therefore do not require elaboration in this text. The specific content and format of these reports, of course, does not form any part of the present invention. What is important in relation to the practice of the present invention is (1) that this content has been gathered in a multifaceted, simultaneous fashion, and (2), has been so gathered, insofar as the anatomical mechanical data is concerned, in a three-dimensional vector manner to provide three axis magnitude and directional information, either externally or internally relative to a subject's anatomy.